Building a LED writing board (marker board)

[CSM]

I want to build a LED writing board.

It's basically a marker board with a LED light behind it and it takes advantage of special fluorescent markers.

My question is, how can I achieve that the board doesn't light up unless the marker is applied to the board. You can see in the video, that the glass stays black/dark until you write on it... How does that work?

https://www.youtube.com/watch?v=pQwdWvGIq5A

 

[pranam77]

A plexi glass is used with a black background where the Edge is lit with RGB LEds. Normally the background will not reflect any light as it is black. As the top surface gets the writing with a pen, the ink which is now on the surface of the plexiglas, starts reflectng the light of the LED's and you get an eye catching display. Simple logic for ashonishing display. Isnt it?.......Cheers

 

[betwixt]

Although you can see some light at the edges, I suspect some of the LEDs may be UV. They give a brighter glow from the fluorescent ink without making the background any lighter.

Yes, they are impressive!

Brian.

 

[CSM]

Thanks for your reply.
I really like your explanation. I got one on another forum too.
My plan is to build them both ways (I prefer the simpleness and cheapness of yours though ).

From: lemonieDate: Mar 24, 2010. 2:14 PMSubject: https://www.instructables.com/community/LED-White-board/

If it's UV backlit, with a visible filter, all you "see" is UV, except you don't because that's outside of your visual range. Apply fluorescent marker and it fluoresces, the UV energy is redistributed and most of it converts to visible. UV backlight, glass
L

 

[KJ6EAD]

These devices make use of frustrated total internal reflection (FTIR): Total internal reflection - Wikipedia, the free encyclopedia along with UV light and fluorescent markers.

 

[ibitechs2005]

please post the marker board circuit for us to see and contribute to its success.